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G. G. CRAWFORD.

} TELEPHONE SYSTEM. APPLICATION FILED ocr. 23. 1918.

1,386,69m Patented Aug. 9,1921,

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GUSTAVUS G. CRAWFORD, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION 013 NEW YORK.

TELEPHONE SYSTEM.

Patented Aug. 9, 1921.

Application filed October 23, 1918. Serial No. 259,364.

To all whom it may concern:

Be it known that I, GUs'rAvUs'C. CRAwr0111), a subject of the King of Great Britain, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Telephone Systems, of which the following is a full,.clear, concise, and exact description.

This invention relates tortelephone systems and more particularly to party tele phone transmission lines employing grounded electromagnetic devices for signaling purposes. i r I In such systems it is desirable to provide electromagnetic signaling devices, such as ringers, at the various stations connected to the telephone line which readily respond to the proper low frequency signaling current without interfering with the telephone transmission over the line circuits. However, it is desirable that such grounded ringer paths efiectively prevent the passage therethrough of talking or other currents of relatively high frequencies which may be impressed on the line conductors so that the metallic transmission line may be substantially free of grounded connections at such frequencies.

It is the object of thisinvention to provide a system of this character wherein the impedance of the grounded electromagnetic device increases materiallyat the frequency ofthe talking or other currents encountered in telephonic transmission, thereby preventing the passage of such currents through the devices. V

In order to attain this object, in accordance with one feature of the invention, a telephone line isiprovided with a ringer or other electromagnetic device the impedance of which is abnormally increased at high frequencies by the use of a supplementary laminated core of low reluctance, and high resistance, providing an increased core surface which is particularly effective at such frequencies. I w

These and other features not specifically mentioned above will appear more fully from the following specification and the annexed drawing, in which Figure 1 shows an elevation of one-construction of an electromagnetic ringer, which may be used in ,con nection with the system, a portion of-one spool of the ringer being shownv as broken through the winding of an electromagnetic device permeates and is distributed throughout the core, the distribution of flux produced by periodically varying currents is materially affected by the frequency of the current, so that at very high frequencies the flux does not penetrate the core to any appreciable depth, producing what is termed magnetic skin effect. Therefore, at high frequencies, the impedance of a device of th1s character is dependent upon the extent of the surface of the core rather than upon its cross-section. It is this principle which is employed in the present system, wherein the effective core is increased for the high frequencies with a resultant abnormal increase in impedance.

One structure which has been found desirable to use in such a system is shown in Figs. 1 and 2 of the accompanying drawing, in which an ordinary biased ringer 1 is shown; each core 2, 2 thereof being equipped with two substantially semi-cylindrical sleeves 3,

,3 of a magnetic material preferably silicon steel possessing low reluctance and high resistance such as are shown in Fig. 2. In Fig. 3 a telephone transmission line A is shown provided with stations B, C, D and E, each of which may be equipped with a ringer 1 of the type shown in Fig. 1. The line A terminates at the central oflice in the jack 1, and a link circuit F of any usual type'terminating in plug .5, is provided atsuoh central office for connection with the line circuit. The link circuit F is provided with keys 6, 7, 8 and 9, adapted for applying suitable periodically varying signaling currents to the line for the selective operation of the ringers at the stations B, C, D and E. I I

It will be observed that in each of the composite cores of the ringer illustrated in Figs. 1 and 2, the inner and outer surfaces of the supplementary core members 3, 3 present agreatly increased surface for, the

distribution of flux without materially increasing the cross-section of the core, thus providing the larger surface desired for abnormally increasing the impedance at the high frequencies. It is desirable that the supplementary core be laminated and possess a high resistance for the well-known purpose of eliminating losses resulting from local currents present therein. Such laminations are provided in the embodiment shown in Figs. 1 and 2, by the use of members 3, 3 which are slightly'less than semi-cylindrical, thus insuring at least one air gap therebetween when they are assembled on the normal cores 2, 2 of the ringer 1.

It is thought that the invention may be more fully comprehended from the follow} ing description of the operation of the system shown in Fig. 8..

Assuming that the operator desires to signal the stationB, the plug 5 is inserted in jack 4- of line A and the key 8 is actuated, thereby connectinga source of periodically varying signaling current through the alternate contact of key 8, the ring contacts of plug 5 and jack 4, the ring conductor of the line A, and the windings of the ringers 1, 1 at stations .13 and C in'parallel, to ground. The ringer at station B being adapted to respond to the character of current supplied over the circuit just traced, operates, while the ringer at station C being unresponsive thereto, does not operate. In case the operator desires to signal the station C, the procedure' is the same as previously described, except'that the key 9 is actuated instead of thefkey 8, and periodically varying current ota character adapted to operateringer at station C is applied to the ring conductor of theline, whereupon such ringer'operates, while the ringer at station E is unresponsive thereto. In a similar manner in case the operator desires to call the station D, the key 6 of the link circuit is actuated to connect a source of periodically varying current similar to the first mentioned source through the alternate contact of key 6," the tip con tacts of plug 5 and jack 4, the tip conductor of line A and the ringers 1,1 at stations D and E in parallel, to ground. The ringer .at station D operates due to the flow of such current, while the ringer at station E.

is unresponsive thereto. In case the station E is to be called,-the procedure is the same, except that key 7 is actuated instead of the key 6, thereby supplying current of a different character to the circuit just traced, causing theresponse of the ringer at station E, while the ringer at'station D does not operate. In any of the above men- I tioned cases, the operator at the central 7 office mayj'connect the telephone set thereat to the linkcircuit F bythe actuation of .the-listeningkey 10 and, after the: response maybe impressedupon theline from eX- traneous-sources, that the grounded paths including such ringers do not affect the transmission over the metallicf'line circuit by the'introduction of noise.

What claimed is: 1. A telephone system comprising a me tallic telephone line, a plurality of stations thereon,'a plurality of grounded branches connected to a conductor of the line, electromagnetic devices included in said branches and means for automatically and abnormally increasing the impedance of such devices during conversation over the line between the stations, said means consisting of a supplementary laminated core.

2. A telephone system comprising a metallic-telephone line, a plurality of stations thereon, a grounded electromagnetic signaling device connected to a conductor of the line at each station, a grounded source of signaling current, switching means for apeplying such current to the conductor to operate the signaling device, a grounded source of current adapted for connection to the. line,

an electromagnetic signaling device and means responsive to the connection of the second source of current for abnormally increasing the impedance of said signaling dccurrent to themetallic line, said meansconsistlng of a supplementary laminatedfcore. v 8. A telephone system comprising atelevice to such current, thereby confining such phone line, a plurality of stations thereon, a V

plurality of grounded electromagnetic signaling devices connected to the line, a source of current for operating the devices, a source of talking current, and means responsive to the connection of'the source of talkingcurrent to the line. for abnormally increasing the impedance of the devices to suchcurrent,

thereby eifecti'vely preventing the'pas'sage of such current through the'devices, said means consisting of a supplementary laminated g4, Atelephonesystem comprising a telephone line,'a-pl-urality of stations thereon a plurality of grounded electromagnetic signaling devices connected to the l-inefand,

adapted for operation upon low frequency 7 cans consistingfof a supplementary 1animatedcore. l' j 5. A telephone systenrcomprising a tele-r phone line, a plurality of stations thereon, a plurality of grounded electromagnetic signaling devices connected to the line and adapted for operation upon low frequency currents, and means for abnormally increasing the impedance of such devices to currents of high frequencies when such high frequency currents are applied to the line said means consisting of two substantially semi-cylindrical magnetic sleeve members superposed on the core thereof.

6 A telephone system comprising a telephone line, a plurality of stations thereon, a plurality of grounded electromagnetic signaling devices connected to the line and adapted for operation upon low frequency currents, and means for abnormally increasing the impedance of such devices to ourrents of high frequencies when such high frequency currents are applied to the line, said means consisting of two substantially semi-cylindrical magnetic sleeve members placed on the core with a longitudinal nonmagnetic gap between such members.

7 The combination with a telephone line of a talking'circuit including the line, a branch circuit including an electromagnetic signaling device connected to the line, and means for abnormally increasing the impedance of the signaling device to currents of talking frequency, said means consisting of a supplementary laminated core.

In witness whereof I hereunto subscribe my name this 18th day of Otcober, A. D.

GUSTAVUS G. CRAWFORD. 

